Surface electromyography electrode assemblies have a variety of industrial uses. Their primary application, however, is concentrated in the psychological, academic research and medical professional fields. For example, psychologists use EMG biofeedback to help patients learn to relax certain muscles, as an aid in overall relaxation. Academic researchers, on the other hand, use EMG measurements to study the impact of muscle contractions on human movement and biomechanics.
Medical professionals employ EMG biofeedback to help patients retrain damaged or atrophied muscles. This can include those recovering from neurological damage as well as those recovering from prolonged inactivity (e.g. post surgery).
Such retraining can be difficult, in part, because the human body will often engage and strengthen surrounding undamaged muscles as substitutes for damaged muscles in order to protect the damaged muscle from re-injury. This can be particularly problematic when the patient is not able to “sense” which muscle is contracting, the injured muscle or the one being substituted.
For example, the Vastus Medialis Oblique (VMO) and Vastus Lateralis (VL) muscles are both part of the quadriceps or “thigh” muscle group. Both muscles attach to the patella, or “kneecap”. Both muscles contract when a seated patient raises his/her leg from the perpendicular (to the ground) to the horizontal (fully extended) position. However, in addition to pulling the patella in the proximal (toward the hip joint) direction, these two muscles also pull in the medial (toward the midline of the body) and lateral (away from the midline of the body) directions. When the forces of these medial and lateral pulls are balanced, the patella “tracks” along its groove at the distal (away from the hip joint) end of the femur without excess wear on either side. Patients often have difficulty consciously choosing the relative amount of contraction between these two muscles.
When one of these two muscles is atrophied, for example the VMO, the body protects the atrophied muscle by over-utilizing a substitute, in this case the VL. As a result, the patella is pulled to one side, causing excessive wear. In addition, this substitution pattern tends to defeat the purpose of therapeutic exercises: instead of strengthening the targeted muscle (VMO) it can serve to increase the strength of the substituted VL muscle instead. The application of EMG biofeedback, however, has been shown to improve the patient's ability to perform their exercises while avoiding the muscle substitution effects.